WO2008015952A1

WO2008015952A1 - Mold release sheet

Info

Publication number: WO2008015952A1
Application number: PCT/JP2007/064649
Authority: WO
Inventors: Tetsuya Yuki; Yoshiaki Hirose
Original assignee: Toyo Tanso Co., Ltd.
Priority date: 2006-07-31
Filing date: 2007-07-26
Publication date: 2008-02-07
Also published as: US8097331B2; JP2008031020A; JP4388041B2; KR20090046748A; TWI391352B; CN101489943A; US20090324886A1; KR101331647B1; EP2055681A4; TW200806598A; EP2055681A1

Abstract

[PROBLEMS] To provide a mold release sheet made of expanded graphite which is useful in pressing silicon carbide, aluminum nitride, or the like and which makes it possible to keep the quality of products at a high level and brings about dramatic enhancement in the working efficiency or the yield. [MEANS FOR SOLVING PROBLEMS] A mold release sheet (4) made of expanded graphite to be applied between the inside face of the outer member (1b) of a mold and silica powder (M), characterized in that the gas permeability as defined by the formula (1) is 1.0 × 10-4cm2/s or below: gas permeability = Q L/(ΔP A)...(1) wherein Q is flow rate (Pa cm3/s) of gas; ΔP is pressure difference (Pa) between two chambers; A is gas permeation area of mold release sheet, that is, area (cm2) of the passageway connecting the two chambers; and L is thickness (cm) of mold release sheet.

Description

Specification

Release sheet

Technical field

[0001] The present invention relates to a release sheet, and more particularly to a release sheet used to improve mold separation when a molded product is removed from a mold to be molded.

Background art

[0002] When manufacturing a member made of silicon carbide or aluminum nitride or the like, a material such as silicon carbide is heated and pressurized in a state where the raw material such as silicon carbide is housed in a graphite mold or a graphite molding container or the like. Mold into the shape of the mold. During such molding, if the raw material is directly heated into a mold or the like and heated, both the raw material and the mold become very hot. Therefore, damage to the mold due to the reaction between the two and the raw material due to impurities contained in the mold or the like. Contamination occurs. In addition, if molding is performed in a state where the raw material evaporative gas or the like is in contact with the raw material, bubbles will be generated in the manufactured product, causing problems when the quality deteriorates.

In view of the above, conventionally, a release sheet is interposed between a mold for molding a substance and a raw material. For example, in the production of quartz glass, silica powder and graphite A felt material made of graphitic carbon fiber is interposed between the mold and the graphite sheet (see, for example, the following patent documents;! To 3).

[0004] Specifically, in Patent Documents 1 and 2, the force and density are 0.;! To 1.5 g / cm ³ and each impurity of Na, K, Fe and Ti is lppm. It is stated that the use of highly purified graphite felt or graphite sheet is used to achieve the following! Graphite felt and graphite sheet are both stretchable and breathable, and the graphite sheet is less lost due to the reaction with the silica powder. There is a statement that it is suitable for producing.

[0005] Further, Patent Document 3 discloses that a force and density of a graphitized force-bonded fiber at the contact portion between the filled silica powder and the cylindrically configured graphitic carbon is 0 .;! To 0.5 g / It is stated that a bon felt with a force of cm ³ is interposed. And, Kiichi Bonfelt has a function of discharging the evaporated silica gas and the gas generated by the reaction of Kiichi Bonfelt and silica. In addition, since it absorbs the difference in thermal expansion between the produced glass and the cylindrically-structured graphite graphite, there is a description that it also has a role of preventing both of them from being destroyed during cooling after glass production.

Patent Document 1: Japanese Patent Application Laid-Open No. 11 228166

Patent Document 2: JP-A-11 278857

Patent Document 3: Japanese Patent Laid-Open No. 10-167742

Disclosure of the invention

Problems to be solved by the invention

[0007] However, in Patent Documents !! to 3, graphite felt, graphite sheet, and carbon felt (hereinafter collectively referred to as “sheet” in some cases) have a certain degree of stretchability and air permeability. However, since these characteristics are not sufficient, there is no way to solve the problem caused by the damage caused by the difference in thermal expansion between the mold and glass or the occurrence of bubbles in the product.

[0008] Further, when a manufactured product is taken out from the mold, a phenomenon that the sheet is attached to the product occurs, and thus it is necessary to remove the sheet from the product. Since such a sheet removal requires a long time, there is a problem that the production efficiency of the product is lowered. However, Patent Documents 1 to 3 do not describe any method for solving such a problem.

[0009] Furthermore, when the sheet adheres to the manufactured product, the unevenness of the sheet surface is transferred to the product surface even if the sheet is removed from the product. In this case, if the transferred unevenness is large, more parts are removed from the product, so that the work time for removing the unevenness becomes longer and the production efficiency further decreases. In addition, the product may be scraped when the sheet is removed. However, if the amount of removal is increased, the thickness of the product becomes thinner than the specified value and the yield of the product is lowered. With respect to this point, conventionally, in Patent Document 1, there is a description that the graphite sheet has a smooth surface and is suitable for obtaining the flatness of the glass surface. If this will shorten the unevenness removal work and improve the yield! /, There are no specific suggestions.

[0010] On the other hand, there is an expanded graphite sheet as a material having stretchability and breathability, and the expanded black lead sheet has flexibility, compressibility, and breathability, and is a preferable property as a release sheet. However, there are no examples that specifically considered and studied the properties that are desirable for application as a release sheet.

[0011] In view of the above circumstances, the present invention can keep product quality high when manufactured by compressing and compressing silicon carbide, aluminum nitride, and the like, and dramatically improve working efficiency and yield. It is an object to provide a release sheet made of expanded graphite

Yes

Means for solving the problem

[0012] In order to achieve the above object, the present invention provides a release sheet that is disposed between a mold and a forming raw material and is made of expanded black lead, and has a gas permeability represented by the following formula (1). 1. equal to or less than ^{^{0 X 10- 4 cm 2 / s}} .

Gas permeability = Q 'L / (A P' A) '' '(1)

In the above equation (1), Q is the gas flow rate (Pa 'cm ³ / s), Δ Ρ is the pressure difference (Pa) between the two chambers, and A is the gas permeation area of the release sheet, that is, The area of the passage connecting the two chambers (cm ² ), L is the thickness (cm) of the release sheet.

If the gas permeability of the release sheet as described above is regulated to be extremely low, in the production of silicon carbide, aluminum nitride, etc., the release sheet is placed between the raw material and the mold. When arranged, it is possible to prevent the gasified raw material or the gas generated by the reaction between the release sheet and the raw material from passing through the release sheet. Accordingly, the reaction between the gas and the mold can be suppressed, so that the mold can be prevented from deteriorating.

[0013] (1) Gas permeability represented by formula is desirably 1. is 0 X 10- ⁹ cm ² / s or more.

From the point of view of suppressing the reaction between the gas and the mold, it is preferable that the gas permeability is low! /. However, if the gas permeability is too low, bubbles are formed in the molded product. Problems such as occurrence S Therefore, it is preferable gas permeability 1. is 0 X 10- ⁹ cm ² / s or more.

[0014] The peel strength shown in the following formula (2) is preferably 50 kPa or less.

Peel strength = LD / (W't) '"(2)

In the above equation (2), LD is the load, t is the thickness of the release sheet, and W is the width of the bonded portion.

If it is regulated so that the peel strength is low as in the above configuration, it can be manufactured from a mold. When a product is taken out, it is possible to remove the sheet adhering to the product easily and quickly. Therefore, the manufacturing cost of the product can be reduced.

[0015] The arithmetic average roughness of the surface is desirably 10 in or less.

If the arithmetic average roughness of the surface of the release sheet as described above is 10 m or less (that is, if the release sheet surface is smooth), the smoothness of the product surface after removal of the sheet is increased. Therefore, the force that does not require processing after removing the sheet is possible, and the working time for processing can be greatly shortened when necessary. Therefore, the production efficiency is greatly improved. In addition, it is possible to prevent the product thickness from becoming thinner than the specified value due to the reduction in the amount of product removed, and the product yield is improved. Furthermore, if the unevenness on the surface of the release sheet is reduced, the variation in thermal conductivity in the surface direction of the sheet is reduced, so that heat can be supplied uniformly to the raw material.

[0016] The thermal conductivity in the plane direction is desirably 100 W bar m'K) or more.

If the thermal conductivity in the surface direction of the release sheet as described above is high, the temperature of the raw material can be raised quickly, so that the molding time can be shortened. As a result, the production efficiency of the product can be reduced. Further improvement.

[0017] It is desirable that the compression ratio represented by the following formula (3) is 30% or more! /.

Compression rate (%) = [(t-t) / t] Χ 100 · · · (3)

1 2 1

In the above equation (3), t is the thickness after applying preload (0.686 MPa ± l%) for 15 seconds.

1

t is the thickness (mm) after applying total pressure (34.3 MPa ± 1%) for 60 seconds. By regulating the compression rate of the release sheet as described above, even if there is a difference in the expansion and contraction amount between the raw material and the mold due to the difference in the thermal expansion coefficient between the raw material and the mold, the release sheet Because the difference can be absorbed by deformation of the product, it is possible to prevent the product or mold from being damaged.

[0018] It is desirable that the compression ratio shown in the above equation (3) is 80% or less! /.

In general, the gas permeability tends to increase as the compression rate increases. If the force compression rate is 80% or less, the gas permeability falls within the above range.

[0019] The force and the density are preferably 0.5 Mg / m ³ or more and 1.5 Mg / m ³ or less.

If the force and density exceed 1.5 Mg / m ³ , the compression rate may decrease, causing damage to the product or mold, or cracking when the release sheet is bent. Density is 0.5Mg If it is less than / m ³ , the gas permeability may increase and the mold may deteriorate.

[0020] The sheet for release according to any one of claims;! To 9, wherein the thickness is 1.5 mm or less.

If the thickness of the release sheet as described above is 1.5 mm or less, the sheet can be easily bent, so attach the release sheet to the mold easily and in close contact. Power S can be. Therefore, the sheet attaching operation can be performed in a short time, and the working time of the entire molding operation can be shortened, so that the manufacturing cost of the product can be reduced.

[0021] The thickness is desirably 0.2 mm or more.

If the thickness of the release sheet as described above is 0.2 mm or more, the release sheet can be prevented from cracking even when the release sheet is bent. This is because the amount of deformation in the thickness direction increases, so that damage to the product or the like can be suppressed.

[0022] Desirably, the ash content is 30 massppm or less! /.

If the amount of ash in the release sheet as described above is small, the raw material to be molded can be prevented from being contaminated, so that the product quality can be improved.

The invention's effect

[0023] As described above, according to the present invention, when silicon carbide or aluminum nitride or the like is manufactured by pressure compression, product quality can be kept high, and work efficiency and yield can be improved. There is an excellent effect that it can be improved.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, an embodiment of the present invention will be described with reference to the drawings.

The mold release sheet of the present invention is obtained when a raw material such as silicon carbide and aluminum nitride is molded by heating and pressing in a state where the raw material is accommodated in a graphite mold, a graphite molding container or the like. It is a sheet | seat used by arrange | positioning between them.

The product manufactured using the release sheet of the present invention is, for example, synthetic quartz or SiC, but is not particularly limited.

[0025] First, before describing the release sheet of the present invention, the use situation of the release sheet of the present invention will be described. Below, the case where cylindrical quartz glass is manufactured is demonstrated as a representative. In FIG. 1, reference numeral 1 denotes a mold in which silica powder M, which is a raw material of quartz glass, is accommodated, and is made of, for example, graphite. The mold 1 is composed of a cylindrical inner member la, a cylindrical outer member lb, and a plate-shaped bottom member lc, and silica powder M is accommodated in a space surrounded by these members. . Reference numeral 2 denotes a pressurizing member for pressurizing the silica powder M.

As shown in FIG. 2, the release sheet 4 of the present invention is disposed on the inner surface of the outer member lb in the mold 1 so that the silica powder M and the mold 1 are not in direct contact with each other. Although not shown, the release sheet 4 of the present invention is also disposed on the inner surface of the inner member la, the upper surface of the bottom member lc, and the lower surface of the pressure member 2 (all surfaces in contact with the silica powder M). Then, if the silica powder M accommodated in the mold 1 is heated while being pressurized by the pressure member 2, a cylindrical synthetic quartz can be formed.

[0027] Next, the release sheet of the present invention will be described.

(Overall configuration of release sheet)

The release sheet of the present invention is formed by molding expanded graphite into a sheet shape. The expanded graphite is formed by immersing natural graphite or quiche graphite in a liquid such as sulfuric acid or nitric acid, and then heat-treating at 400 ° C or higher, and has a cotton-like or fibrous shape. That is, its axial length is greater than its radial length. For example, expanded graphite has an axial length of about 1 to 3 mm and a radial length of about 00 to 600 111. And in the release sheet of the present invention, the expanded graphite is entangled as described above.

The release sheet of the present invention may be formed only from expanded graphite as described above, but a binder such as phenol resin or rubber component is mixed slightly (for example, about 5%)! / Good.

[0028] (Gas permeability of release sheet)

Release sheet of the present invention, the (1) at the indicated gas permeability is adjusted to be ^{^{1. 0 X 10- 4 cm 2 /}} s or less under.

In the manufacture of metal such as silicon carbide or aluminum nitride, the raw material is gasified The problem is that graphite molds are deteriorated by the gas permeating through the release sheet if the gas permeability of the release sheet is too large. To do. However, if the gas permeability of the release sheet is regulated as described above, it is possible to suppress the generated gas from permeating the release sheet, so that the graphite mold is deteriorated (SiC conversion). ) Can be prevented and the life of molds can be extended.

Yes

[0029] However, too small a gas permeability, since problems such as bubbles are generated in the molded product occurs, it gas permeability 1. is 0 X 10- ⁹ cm ² / s or more preferable. Or from the this, the gas permeability of the release sheet is ^{^{1. 0 X 10- 9 cm 2 /}} s or more ^{^{1. 0 X 10- 4 cm 2 /}} s that preferably tool especially following is under 1 . 0 is preferably X 10- ⁹ cm ² / s or more 1. or less ^{^{0 X 10- 6 cm 2 / s}} .

[0030] (Peel strength of release sheet)

The release sheet of the present invention is adjusted so that the peel strength is 50 kPa or less. With such a configuration, when the product is taken out of the mold, the release sheet adhering to the product can be easily removed, so that the post-processing work after product molding can be completed in a short time. Touch with S.

[0031] (Smoothness of release sheet)

When a release sheet is used, the unevenness of the release sheet surface is transferred to the product surface. However, depending on the product to be manufactured, high smoothness is required as the surface property. In the case of such a product, if the smoothness of the surface of the release sheet is low, it is necessary to process the product surface to have a predetermined smoothness after removing the release sheet.

Here, since the release sheet of the present invention is adjusted so that the arithmetic average roughness of the surface thereof is 10 m or less, the shape of the release sheet surface on the molded product, that is, Even if the unevenness is transferred, the smoothness of the product surface after removing the release sheet can be increased.

Therefore, if the smoothness of the surface is high as in the release sheet of the present invention and the smoothness is higher than the smoothness required for the product surface, processing after removing the release sheet becomes unnecessary. The On the other hand, even if the product requires a higher smoothness than the smoothness of the release sheet surface The amount removed from the product by processing can be reduced. Therefore, it is possible to shorten the processing time for achieving the predetermined smoothness, and as a result, the production efficiency of the product is improved. In addition, it is possible to suppress the product thickness from becoming thinner than the specified value due to a reduction in the amount of product removed, which improves the product yield. Furthermore, if the unevenness on the surface of the release sheet is reduced, variation in thermal conductivity in the surface direction of the sheet is reduced, so that heat can be supplied uniformly to the raw material.

[0033] If the following method is employed, the release sheet of the present invention as described above can be produced so that the arithmetic average roughness of the surface thereof is 10 m or less.

First, after immersing natural graphite, quiche graphite or the like in a liquid such as sulfuric acid or nitric acid, heat treatment is performed at 400 ° C. or higher to form cotton-like graphite (expanded graphite). The expanded graphite has a thickness of 1.0 to 30.0 mm and a bulk density of 0;; to 0.5 Mg / m ^3. The expanded graphite has a thickness of 0.2 to 0.6 mm and a bulk density of 0. 5 ~; 1. Compress to 5Mg / m ³ to form a release sheet.

[0034] At this time, if the expanded graphite is compressed by roll rolling at a feed rate of 20. Om / min or less, it is possible to prevent wrinkles and the like from being generated on the surface of the release sheet. It is possible to produce a release sheet having an arithmetic average roughness of the surface of 10 m or less. However, when the feed rate is less than 0.1 lm / min, the productivity of expanded graphite decreases. Therefore, the feed speed is preferably 0.1-20.Om/min. In particular, it is preferable that the feed rate is regulated to 0.5 to 15. Om / min.

[0035] The arithmetic average roughness is defined in JIS B0601. Specifically, as shown in Fig. 3, the arithmetic average roughness (Ra) is extracted from the roughness curve by the reference length L in the direction of the average line, and the X-axis is extracted in the direction of the average line of the extracted portion. On the other hand, when the y-axis is taken in the direction of the vertical magnification and the roughness curve is represented by y = f (X), the value obtained by the following equation 1 is represented by micrometer nore (m)! /, Yeah.

[0036] [Equation 1]

[0037] (Thermal conductivity of release sheet) The release sheet of the present invention is adjusted so that the thermal conductivity in the surface direction is 100 W / (m′K) or more. With such a configuration, the temperature of the raw material rises quickly and the molding time can be shortened, so that the production efficiency is dramatically improved.

[0038] In particular, when the release sheet of the present invention is produced by the method described in the above section (Smoothness of the release sheet), the thermal conductivity in the surface direction becomes uniform. Specifically, a part of the release sheet is cut out to form a square test piece having a side of 200 mm, and in this test piece, the heat in a plurality of square test areas having a side of 25 mm is formed. When the conductivity is measured, the difference between the thermal conductivity value in the test region where the thermal conductivity is maximum and the thermal conductivity value in the test region where the thermal conductivity is minimum is calculated as the thermal conductivity in all test regions. The release sheet can be manufactured so that the value divided by the average value of the ratio is 0.1 or less. Then, the formation of heat spots on the release sheet can be prevented, so that the product can be heated uniformly and a more homogeneous product can be produced.

[0039] (Compression rate of release sheet)

In addition, the release sheet of the present invention is adjusted so that the compression ratio represented by the formula (3) is 30% or more.

With such a configuration, even if there is a difference in the expansion / contraction amount between the raw material and the mold or the like at the start of heating or cooling due to the difference in the thermal expansion coefficient between the raw material and the mold or the like, the difference is reduced. Since the release sheet can be deformed and absorbed, damage to products and molds can be prevented.

[0040] (Thickness and bulk density of release sheet)

Even if the release sheet of the present invention has the above-described compression rate, if the thickness is too thin, it is not possible to take a sufficient cushioning. In other words, there is a possibility that the difference between the expansion and shrinkage of the raw material and the mold cannot be absorbed! /.

When the release sheet of the present invention is attached between the raw material and the mold, the release sheet is bent and deformed so as to be in close contact with the raw material and the mold. At this time, if the strength of the release sheet itself is weak or its flexibility is low, even if the release sheet has the compression ratio as described above, the release sheet is bent and deformed. It can crack, chip or tear itself. However, if the release sheet of the present invention has a thickness of 0.2 mm or more and 1.5 mm or less, and a force and a bulk density of 0.5 Mg / m ³ or more and 1.5 Mg / m ³ or less, Since the release sheet has a certain degree of strength, even if the release sheet is deformed, it can be prevented from cracking. In addition, since the release sheet is not too thick, the release sheet can be easily bent and can be prevented from cracking even if it is bent. For this reason, it is possible to easily attach the release sheet to a mold or the like, and it is possible to attach the release sheet in a state of being in close contact with the mold or the like.

[0041] Therefore, since the work for attaching the release sheet can be performed in a short time, it is possible to contribute to shortening the work time of the entire molding work by simply attaching the release sheet. Monkey.

In particular, the release sheet, the thickness of 0. 3 mm or more 1. 5 mm or less, moreover, if the bulk density 0. 5 Mg / m ³ or more 1. and 5 mg / m ³ or less, the bending of the release sheet Since the strength is high while maintaining the properties, cracking of the release sheet can be prevented more reliably, which is preferable.

[0042] (Ash content of release sheet)

Further, in the production process of the release sheet of the present invention, the release sheet is processed by adjusting the release sheet so that the ash content in the release sheet is 30 ppm or less by treating with release gas, rogen gas, or the like. Since the content of ash in the inside is small, it is possible to prevent the molding material from being contaminated and to improve the quality of the molded product.

Example

[0043] (First Example)

The relationship between gas permeability and bulk density in the release sheet of the present invention was examined, and the results are shown in FIG.

The measurement was performed on a release sheet having a thickness of 0.5 mm and an arithmetic average roughness of the surface of 10 m or less, and the force and the density were 0.1, 0.3, 0.5, 0.7, 1. The gas permeability was confirmed at 0, 1.5, and 1.7 Mg / m ³ .

The release sheet is adjusted with halogen gas so that the ash content is 30 ppm or less.

[0044] Gas permeability was measured by the following method. (1) In a pair of sealed chambers CA and CB communicated with each other, the passage (diameter 10 mm) communicating both chambers CA and CB is closed with the release sheet (diameter 30 mm) of the present invention. To do. In other words, air does not flow between the pair of sealed chambers CA and CB unless they pass through the release sheet of the present invention.

[0045] (2) from this state, both chambers one CA, the air pressure in the CB is evacuated both Chiya members CA, CB until 1 · 0 X 10- ⁴ Pa. Then, while evacuating the one chamber CA, N gas is supplied until the other chamber CB reaches a predetermined pressure (1.0 × 10 ⁵ Pa).

(3) When the pressure in the other chamber CB reaches a predetermined pressure (1 · 0 × 10 ⁵ Pa), the evacuation in one chamber CA is stopped. Then, according to the pressure difference between the two chambers CA and CB and the gas permeability of the release sheet, N gas gradually flows from the other chamber CB to one chamber CA. The pressure in the CA rises.

[0047] (4) Then, after stopping the evacuation in one chamber CA, the pressure rise rate in one chamber CA for about 100 seconds is measured, and based on the following equation (1): The gas permeability K (cm ² / s) was calculated.

[0048] Gas permeability K = Q 'L / (A P' A) · · · · (1)

In the above equation (1), Q is the gas flow rate (Pa 'cm ³ / s), Δ Ρ is the pressure difference (Pa) between the two chambers, and A is the gas permeation area of the release sheet, that is, The area of the passage connecting the two chambers (cm ² ), L is the thickness (cm) of the release sheet. Further, the gas flow rate Q is calculated from the pressure increase rate in one chamber CA and the volume of one chamber CA for about 100 seconds after the evacuation in one chamber CA is stopped.

As shown in FIG. 4, it can be confirmed that the gas permeability decreases as the force and the density increase, in other words, the gas shielding performance increases as the force and the density increase.

[0050] (Second embodiment)

The relationship between peel strength and bulk density in the release sheet of the present invention was examined, and the results are shown in FIG.

The measurement was performed on a release sheet having a thickness of 0.5 mm and an arithmetic average roughness of the surface of 10 m or less. The force and the density were 0.3, 0.6, 0.8, 1.0, 1. 2, 1.4, 1. 6, 1.8, 2. OMg / m ³ The peel strength was checked. The release sheet is adjusted with halogen gas so that the ash content is 30 ppm or less.

[0051] Here, a method for measuring the peel strength of the release sheet of the present invention will be described.

5 to 7 are diagrams illustrating a method for measuring the peel strength. 5 to 7, reference numeral 4 denotes a release sheet of the present invention. As shown in FIG. 7, the peel strength was measured by attaching one end of tape 5 having an adhesive layer such as damplon tape to the surface of one end of release sheet 4 This is done by pulling the end part and the other end part of the tape 5 and measuring the load when they are separated.

[0052] (1) Preparation method of test piece

First, as shown in FIG. 5, one end of the release sheet 4 of the present invention and one end of the tape 5 are pasted so that the bonded portion has a width W25 mm × a length OL10 mm (width W, length OL). For example, see Fig. 6 and Fig. 7), and a crimping tool such as a roller (crimping speed approx. 5mm / s, 1 reciprocation).

[0053] After the release sheet 4 and the tape 5 were pressure-bonded in this way, the tape 5 was folded back with one end portion of the tape 5 attached as shown in FIG. At this time, care should be taken so that the surface of the folded tape 5 is parallel to the attached surface, that is, the surface of the release sheet 4.

Finally, the release sheet 4 and the tape 5 were cut and adjusted so that the entire length L of the test piece 10 was 100 mm.

[0054] (2) Method of measuring peel strength using test piece 10

First, as shown in Fig. 7, attach both ends of the specimen to Chuck C and hold the specimen so that it is horizontal. Then, load is applied in a direction in which both ends of the specimen are separated at a uniform speed V [20 (mm / min)]. That is, the both ends of the test piece 10 are pulled away from each other.

[0055] When the load applied to the test piece 10 is increased, the tape 5 of the test piece 10 is peeled off from the release sheet 4 in due course. Based on the following formula (2), the peel strength T of the release sheet 4 is obtained from the load LD when the peeling starts.

T = LD / (W-t) (2)

In the formula (2), t is the thickness of the release sheet 4 and W is the width of the bonded portion. [0056] As the tape 5, Dumplon Tape No. 3505 (manufactured by Nitto Denko Corporation) was used. Furthermore, a tester Instron 4301 is used as a measuring machine, and the release sheet 4 of the present invention is attached to the upper chuck of the tester, the tape 5 is attached to the lower chuck, and the test piece is mounted horizontally. 20 Apply a load at a uniform speed of (mmZmin), record the maximum value at which peeling occurs between the two, and based on this load! The peel strength was determined.

In addition, the start of peeling was judged by the force and torque applied to the apparatus.

[0057] As shown in FIG. 8, the peel strength increases as the force and bulk density increase, and the bulk strength increases rapidly between 1 · 4 and 1; 6 Mg / m ^3. It can be confirmed that it is connected.

[0058] (Third embodiment)

The compression ratio when the release sheet of the present invention was pressurized and compressed from the thickness direction at a pressure of 34.3 MPa was examined, and the relationship between force, bulk density, and compression ratio was confirmed. Shown in 9.

Measurements were made on a release sheet with a thickness of 0.5 mm, and the force and thickness were 0.1, 0.5, 0.8, 1.0, 1.2, 1.5, 1.8 Mg / m ³ The compression ratio was measured.

As shown in Fig. 9, it can be confirmed that the compression ratio decreases as the force density increases.

[0059] (Example 4)

The variation in thermal conductivity of the release sheet of the present invention having a thickness of 0 · 2 to 0.6 mm and a force density of 0.5 to 5: 1. 5 Mg / m ³ was compared. Show.

The variation in thermal conductivity was determined by cutting nine 25 x 25 mm test pieces from the release sheet of the present invention of 200 x 200 mm, and the maximum value of the thermal conductivity in the surface direction of each test piece (Max) And the difference between the minimum value (Min) and average heat conductivity (Ave.).

[0060] [Table 1]

Note that the unit of the surface orientation is WZ (m · K). [0061] As shown in Table 1, the variation in the thermal conductivity of the release sheet of the present invention was 0.1 or less, and it was confirmed that the thermal uniformity was excellent.

Industrial applicability

[0062] The release sheet of the present invention is suitable for a sheet used to prevent damage to the mold or contamination of raw materials in the production of silicon carbide (SiC), aluminum nitride, synthetic quartz, or the like.

FIG. 1 is a schematic explanatory diagram of equipment for producing synthetic quartz and the like.

FIG. 2 is an enlarged cross-sectional view of part A in FIG.

FIG. 3 is a graph for explaining surface roughness.

FIG. 4 is a graph showing the relationship between force, bulk density and gas permeability in a release sheet.

FIG. 5 is an explanatory view showing a method for producing a test piece used for peel strength measurement.

FIG. 6 is an explanatory view showing a method for producing a test piece used for peel strength measurement.

FIG. 7 is an explanatory diagram showing a method for measuring peel strength.

FIG. 8 is a graph showing the relationship between force, density, and peel strength in a release sheet.

FIG. 9 is a graph showing the relationship between force, bulk density and compressibility in a release sheet.

Explanation of symbols

[0064] 1 Monoredo

4 Release sheet

M Silica powder

Claims

The scope of the claims

[1] A release sheet that is disposed between a mold and a forming raw material and has an expanded graphite force,

Below (1) Gas permeability represented by formula is not more than 1.0X10- ⁴ cm ² / s,

A release sheet characterized by that.

Gas permeability = Q'L / (AP'A) '' '(1)

In the above equation (1), Q is the gas flow rate (Pa'cm ³ / s), ΔΡ is the pressure difference (Pa) between the two chambers, and A is the gas permeation area of the release sheet, that is, 2 The area of the passage connecting the two chambers (cm ² ), L is the thickness (cm) of the release sheet.

[2] above (1) is gas permeability 1.0X 10- ⁹ cm ² / s or more represented by formula, a release sheet of claim 1, wherein.

[3] The release sheet according to claim 1 or 2, wherein the peel strength represented by the following formula (2) is 50 kPa or less.

Peel strength = LD / (W't) '"(2)

[4] The release sheet according to any one of claims 1 to 3, wherein the arithmetic average roughness of the surface is 10 m or less.

[5] The release sheet according to any one of claims 1 to 4, wherein the thermal conductivity in the plane direction is 100 W bar m'K) or more.

[6] The release sheet according to any one of claims 1 to 5, wherein the compression ratio represented by the following formula (3) is 30% or more.

Compression rate (%) = [(t— t) / t] Χ100 (3)

1 2 1

1

t is the thickness (mm) after 60 seconds of total pressure (34.3 MPa ± 1%) is applied.

[7] The release sheet according to claim 6, wherein the compression ratio represented by the formula (3) is 80% or less.

[8] The release sheet according to any one of claims 1 to 7, wherein the force and density are 0.5 · 5 Mg / m ³ or more and 1.5 · 5 Mg / m ³ or less.

[9] The release sheet according to any one of claims 8 to 8, which has a thickness of 1.5 mm or less.

[10] The release sheet according to claim 9, wherein the thickness is 0.2 mm or more.

[11] The mold for release according to any one of claims 1 to 10, wherein the ash content is 30 massppm or less.